Middle threaded fitting

ABSTRACT

A fitting for forming a double-walled tube includes an inner fitting having a first inner weld lip, a second inner weld lip, and an inner body extending from the first inner weld lip to the second inner weld lip and having an outer surface with a first threading. The fitting also includes an outer fitting having a first outer weld lip, a second outer weld lip, and an outer body extending from the first outer weld lip to the second outer weld lip and having an inner surface with a second threading that is configured to mate with the first threading.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/631,809, filed Jun. 23, 2017 for “MIDDLE THREADED FITTING”, which ishereby incorporated by reference herein.

FIELD

The present disclosure is directed to a double-walled tube and, moreparticularly, to a fitting having multiple pieces for forming adouble-walled tube.

BACKGROUND

Gas turbine engines include a compressor section for compressing air, acombustor section for mixing the compressed air with fuel and combustingthe mixture to generate exhaust, and a turbine section for convertingthe exhaust into torque. Portions of the compressor section, thecombustor section, and the turbine section may include parts that moverelative to adjacent parts. In that regard, it is desirable to providelubrication to many of these locations. Double-walled tubes may beutilized throughout gas turbine engines to transport a lubricatingfluid, such as oil. The inner tube may transport the fluid, and apassageway between the inner tube and the outer tube may collect andtransport fluid that leaks from the inner tube to reduce the likelihoodof the lubrication flowing freely within the gas turbine engine.

SUMMARY

Disclosed herein is a fitting for forming a double-walled tube. Thefitting includes an inner fitting having a first inner weld lip, asecond inner weld lip, and an inner body extending from the first innerweld lip to the second inner weld lip and having an outer surface with afirst threading. The fitting also includes an outer fitting having afirst outer weld lip, a second outer weld lip, and an outer bodyextending from the first outer weld lip to the second outer weld lip andhaving an inner surface with a second threading that is configured tomate with the first threading.

In any of the foregoing embodiments, the inner fitting further includesat least two bump-outs extending outward from the inner body, and theouter surface with the first threading is positioned on an outer surfaceof the at least two bump-outs.

In any of the foregoing embodiments, a channel is defined between the atleast two bump-outs when the inner fitting is mated with the outerfitting to allow fluid to flow between the inner body and the outerbody.

In any of the foregoing embodiments, the at least two bump-outs includesthree bump-outs.

In any of the foregoing embodiments, the outer fitting further includesan outward-extending protrusion having at least one angle configured tointerface with a tool for fastening the outer fitting to the innerfitting.

In any of the foregoing embodiments, the outward-extending protrusionhas a shape that corresponds to a portion of a hexagon.

In any of the foregoing embodiments, a length of the inner fitting fromthe first inner weld lip to the second inner weld lip is less than alength of the outer fitting from the first outer weld lip to the secondouter weld lip.

Also described is a double-walled tube. The double-walled tube includesan inner tube having a first inner tube, a second inner tube, and aninner fitting having a first inner weld lip configured to be welded tothe first inner tube, a second inner weld lip configured to be welded tothe second inner tube, and an inner body extending from the first innerweld lip to the second inner weld lip and having an outer surface with afirst threading. The double-walled tube further includes an outer tubehaving a first outer tube, a second outer tube, and an outer fittinghaving a first outer weld lip configured to be welded to the first outertube, a second outer weld lip configured to be welded to the secondouter tube, and an outer body extending from the first outer weld lip tothe second outer weld lip and having an inner surface with a secondthreading that is configured to mate with the first threading.

In any of the foregoing embodiments, the inner fitting further includesat least two bump-outs extending outward from the inner body, and theouter surface with the first threading is positioned on an outer surfaceof the at least two bump-outs.

In any of the foregoing embodiments, a channel is defined between the atleast two bump-outs when the inner fitting is mated with the outerfitting to allow fluid to flow between the inner body and the outerbody.

In any of the foregoing embodiments, the inner tube is configured totransport the fluid and the channel is configured to allow leakage fluidfrom the inner tube to pass between the outer fitting and the innerfitting.

In any of the foregoing embodiments, the at least two bump-outs includesthree bump-outs.

In any of the foregoing embodiments, the outer fitting further includesan outward-extending protrusion having at least one angle configured tointerface with a tool for fastening the outer fitting to the innerfitting.

In any of the foregoing embodiments, the outward-extending protrusionhas a shape that corresponds to a portion of a hexagon.

In any of the foregoing embodiments, a length of the inner fitting fromthe first inner weld lip to the second inner weld lip is less than alength of the outer fitting from the first outer weld lip to the secondouter weld lip.

Also described is a gas turbine engine. The gas turbine engine includesa compressor section configured to compress air. The gas turbine enginealso includes a combustor configured to receive compressed air from thecompressor section and fuel and ignite the compressed air and the fuelto generate exhaust. The gas turbine engine also includes a turbinesection configured to convert the exhaust into torque. The gas turbineengine also includes a double-walled tube configured to transport fluidthrough a portion of at least one of the compressor section or theturbine section. The double-walled tube includes an inner tube having afirst inner tube, a second inner tube, and an inner fitting having afirst inner weld lip welded to the first inner tube, a second inner weldlip welded to the second inner tube, and an inner body extending fromthe first inner weld lip to the second inner weld lip and having anouter surface with a first threading. The double-walled tube alsoincludes an outer tube having a first outer tube, a second outer tube,and an outer fitting having a first outer weld lip welded to the firstouter tube, a second outer weld lip welded to the second outer tube, andan outer body extending from the first outer weld lip to the secondouter weld lip and having an inner surface with a second threading thatis configured to mate with the first threading.

In any of the foregoing embodiments, the inner fitting further includesat least two bump-outs extending outward from the inner body, a channelis defined between the at least two bump-outs to allow the fluid to flowbetween the inner body and the outer body, and the outer surface withthe first threading is positioned on an outer surface of the at leasttwo bump-outs.

In any of the foregoing embodiments, the inner tube is configured totransport the fluid and the channel is configured to allow leakage fluidfrom the inner tube to pass between the inner fitting and the outerfitting.

In any of the foregoing embodiments, the outer fitting further includesan outward-extending protrusion having a shape that corresponds to aportion of a hexagon and is configured to interface with a wrench forfastening the outer fitting to the inner fitting.

In any of the foregoing embodiments, a length of the inner fitting fromthe first inner weld lip to the second inner weld lip is less than alength of the outer fitting from the first outer weld lip to the secondouter weld lip.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be understood, however, the following descriptionand drawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed, non-limiting,embodiments. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a schematic cross-section of a gas turbine engine, inaccordance with various embodiments;

FIGS. 2A and 2B are perspective views illustrating an inner fitting andan outer fitting of a fitting for use in a double-walled tube, inaccordance with various embodiments;

FIG. 2C is an axial view of the fitting of FIGS. 2A and 2B, inaccordance with various embodiments;

FIGS. 3A and 3B are cross-sectional views of the inner fitting and theouter fitting of FIGS. 2A and 2B, in accordance with variousembodiments;

FIG. 3C is a cross-sectional view of the fitting of FIGS. 2A and 2B, inaccordance with various embodiments; and

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F illustrate a method of forming adouble-walled tube using the fitting of FIGS. 2A and 2B, in accordancewith various embodiments.

DETAILED DESCRIPTION

All ranges and ratio limits disclosed herein may be combined. It is tobe understood that unless specifically stated otherwise, references to“a,” “an,” and/or “the” may include one or more than one and thatreference to an item in the singular may also include the item in theplural.

The detailed description of various embodiments herein makes referenceto the accompanying drawings, which show various embodiments by way ofillustration. While these various embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosure, it should be understood that other embodiments may berealized and that logical, chemical, and mechanical changes may be madewithout departing from the spirit and scope of the disclosure. Thus, thedetailed description herein is presented for purposes of illustrationonly and not of limitation. For example, the steps recited in any of themethod or process descriptions may be executed in any order and are notnecessarily limited to the order presented. Furthermore, any referenceto singular includes plural embodiments, and any reference to more thanone component or step may include a singular embodiment or step. Also,any reference to attached, fixed, connected, or the like may includepermanent, removable, temporary, partial, full, and/or any otherpossible attachment option. Additionally, any reference to withoutcontact (or similar phrases) may also include reduced contact or minimalcontact. Cross hatching lines may be used throughout the figures todenote different parts but not necessarily to denote the same ordifferent materials.

As used herein, “aft” refers to the direction associated with theexhaust (e.g., the back end) of a gas turbine engine. As used herein,“forward” refers to the direction associated with the intake (e.g., thefront end) of a gas turbine engine.

As used herein, “radially outward” refers to the direction generallyaway from the central longitudinal axis of a turbine engine. As usedherein, “radially inward” refers to the direction generally towards thecentral longitudinal axis of the turbine engine.

In various embodiments and with reference to FIG. 1, a gas turbineengine 20 is provided. The gas turbine engine 20 may be a two-spoolturbofan that generally incorporates a fan section 22, a compressorsection 24, a combustor section 26 and a turbine section 28. Alternativeengines may include, for example, an augmentor section among othersystems or features. In operation, the fan section 22 can drive coolant(e.g., air) along a bypass flow path B while the compressor section 24can drive coolant along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a turbofan gas turbine engine20 herein, it should be understood that the concepts described hereinare not limited to use with turbofans as the teachings may be applied toother types of turbine engines including three-spool architectures.

The gas turbine engine 20 may generally comprise a low speed spool 30and a high speed spool 32 mounted for rotation about an engine centrallongitudinal axis X-X′ relative to an engine static structure 36 orengine case via several bearing systems 38, 38-1, and 38-2. It should beunderstood that various bearing systems 38 at various locations mayalternatively or additionally be provided, including for example, thebearing system 38, the bearing system 38-1, and the bearing system 38-2.

The low speed spool 30 may generally comprise an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 may be connected to the fan 42 through ageared architecture 48 that can drive the fan 42 at a lower speed thanthe low speed spool 30. The geared architecture 48 may comprise a gearassembly 60 enclosed within a gear housing 62. The gear assembly 60couples the inner shaft 40 to a rotating fan structure. The high speedspool 32 may comprise an outer shaft 50 that interconnects a highpressure compressor 52 and high pressure turbine 54. A combustor 56 maybe located between high pressure compressor 52 and high pressure turbine54. A mid-turbine frame 57 of the engine static structure 36 may belocated generally between the high pressure turbine 54 and the lowpressure turbine 46. The mid-turbine frame 57 may support one or morebearing systems 38 in the turbine section 28. The inner shaft 40 and theouter shaft 50 may be concentric and rotate via bearing systems 38 aboutthe engine central longitudinal axis X-X′, which is collinear with theirlongitudinal axes. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine.

The airflow of core flow path C may be compressed by the low pressurecompressor 44 and the high pressure compressor 52, mixed and burned withfuel in the combustor 56, then expanded over the high pressure turbine54 and the low pressure turbine 46. The turbines 46, 54 rotationallydrive the respective low speed spool 30 and high speed spool 32 inresponse to the expansion.

The gas turbine engine 20 may be, for example, a high-bypass ratiogeared engine. In various embodiments, the bypass ratio of the gasturbine engine 20 may be greater than about six (6:1). In variousembodiments, the bypass ratio of the gas turbine engine 20 may begreater than about ten (10:1). In various embodiments, the gearedarchitecture 48 may be an epicyclic gear train, such as a star gearsystem (sun gear in meshing engagement with a plurality of star gearssupported by a carrier and in meshing engagement with a ring gear) orother gear system. The geared architecture 48 may have a gear reductionratio of greater than about 2.3:1 and the low pressure turbine 46 mayhave a pressure ratio that is greater than about five (5:1). In variousembodiments, the diameter of the fan 42 may be significantly larger thanthat of the low pressure compressor 44, and the low pressure turbine 46may have a pressure ratio that is greater than about five (5:1). The lowpressure turbine 46 pressure ratio may be measured prior to the inlet ofthe low pressure turbine 46 as related to the pressure at the outlet ofthe low pressure turbine 46 prior to an exhaust nozzle. It should beunderstood, however, that the above parameters are exemplary of variousembodiments of a suitable geared architecture engine and that thepresent disclosure contemplates other gas turbine engines includingdirect drive turbofans. A gas turbine engine may comprise an industrialgas turbine (IGT) or a geared engine, such as a geared turbofan, ornon-geared engine, such as a turbofan, a turboshaft, or may comprise anygas turbine engine as desired.

In various embodiments, the low pressure compressor 44, the highpressure compressor 52, the low pressure turbine 46, and the highpressure turbine 54 may comprise one or more stages or sets of rotatingblades and one or more stages or sets of stationary vanes axiallyinterspersed with the associated blade stages but non-rotating aboutengine central longitudinal axis X-X′. The compressor and turbinesections 24, 28 may be referred to as rotor systems. Within the rotorsystems of the gas turbine engine 20 are multiple rotor disks, which mayinclude one or more cover plates or minidisks. Minidisks may beconfigured to receive balancing weights or inserts for balancing therotor systems.

In various embodiments, the gas turbine engine 20 may include adouble-walled tube 70. The double-walled tube 70 may extend through aportion of at least one of the compressor section 24 or the turbinesection 28. For example, the double-walled tube 70 may transport a fluidlubricant, such as oil, between various components of the gas turbineengine 20.

Turning to FIGS. 2A and 2B, the double-walled tube 70 may include afitting 100. An A-R-C axis is shown throughout the drawings toillustrate the axial, radial, and circumferential directions,respectively, of the fitting 100.

The fitting 100 may include multiple pieces including an inner fitting101 and an outer fitting 120. The inner fitting 101 may include a firstinner weld lip 102, a second inner weld lip 104, and an inner body 106extending from the first inner weld lip 102 to the second inner weld lip104.

The inner fitting 101 may further include at least two bump-outs 108extending outward from the inner body 106. Each of the at least twobump-outs 108 may include an outer surface 110 at an outer end 109 ofthe bump-outs 108 facing away from the inner body 106. The outer surface110 of each of the bump-outs 108 may include a first threading 112. Asshown in FIGS. 2A and 2B, the inner fitting 101 includes three bump-outs108.

The outer fitting 120 may include a first outer weld lip 122, a secondouter weld lip 124, and an outer body 126 extending from the first outerweld lip 122 to the second outer weld lip 124.

The outer fitting 120 may include an inward extending flange 130extending radially inward from the outer body 126. The inward extendingflange 130 may have an inner surface 128 facing away from the outer body126. At least a portion of the inner surface 128 may include a secondthreading 132. In various embodiments, the entire inner surface 128 mayinclude threading. Such a design may allow the outer fitting 120 to beplaced in any position relative to the inner fitting 101, while alsoallowing the fitting to be installed from either direction.

The second threading 132 is designed to mate with the first threading112 of the inner fitting 101. In that regard, the inner fitting 101 maybe positioned inside of the outer fitting 120 and may be fastened to theouter fitting 120 via the first threading 112 and the second threading132.

The outer fitting 120 includes an outer surface 129. The outer surface129 may include an outward extending protrusion 134 extending radiallyoutward therefrom. The outward extending protrusion 134 may have a shapethat includes at least one angle 136. In that regard, the outwardextending protrusion 134 may be designed to interface with a tool forfastening the outer fitting 120 to the inner fitting 101.

For example, the outward extending protrusion 134 may have a shape thatcorresponds to a portion of a hexagon. As shown, the outward extendingprotrusion 134 includes two sides of a hexagon. In that regard, a wrench(such as with a full or partial hex socket) may be positioned over theoutward extending protrusion 134 and torqued to fasten the outer fitting120 to the inner fitting 101.

The outer surface 129 may be designed without features at locationscircumferentially opposite of the outward extending protrusion 134. Inthat regard, optional features may be added to the portions of the outersurface 129 circumferentially opposite of the outward extendingprotrusion 134. For example, the optional features may include a bolthole, a mounting flange, or the like in order to mount the outer fitting120 to a structure of the gas turbine engine 20 of FIG. 1.

Referring now to FIG. 2C, the fitting 100 is shown with the outerfitting 120 coupled to the inner fitting 101. As shown, the inner body106 of the inner fitting 101 defines a main flow path 150 through whichfluid may flow. In that regard, the main flow path 150 may transport afluid, such as oil.

Additionally, one or more channel 152 may be defined between each of thebump-outs 108 and between the inner fitting 101 and the outer fitting120. The channels 152 may receive and transport leakage fluid that hasleaked from the main flow path 150.

Referring to FIGS. 3A and 3B, cross-sectional views of the inner fitting101 and the outer fitting 120 are shown. The inner fitting 101 has alength of the inner fitting 200 extending from the first inner weld lip102 to the second inner weld lip 104. Likewise, the outer fitting 120has a length of the outer fitting 202 extending from the first outerweld lip 122 to the second outer weld lip 124. In various embodiments,the length of the inner fitting 200 may be less than the length of theouter fitting 202.

After assembly of the double-walled tube 70, the weld joints may beinspected, such as via x-ray imaging. The weld joints are located at thefirst inner weld lip 102, the second inner weld lip 104, the first outerweld lip 122, and the second outer weld lip 124. Because the length ofthe inner fitting 200 is less than the length of the outer fitting 202,the first outer weld lip 122 and the second outer weld lip 124 may beexamined via x-ray imaging without interference from the inner fitting101.

The inner body 106 has an inner body thickness 204 at locations awayfrom the bump-outs 108 and a bump-out thickness 206 at the bump-outs108. As shown, the bump-out thickness 206 is greater than the inner bodythickness 204.

Similarly, the outer body 126 has an outer body thickness 208 atlocations away from the inward extending flange 130 and a flangethickness 210 at the inward extending flange 130. As shown, the flangethickness 210 is greater than the outer body thickness 208.

Referring to FIG. 3C, the inner fitting 101 is fastened to the outerfitting 120. As shown, the first threading 112 located on the bump out108 is designed to mate with the second threading 132 of the inwardextending flange 130. In that regard, the inner fitting 101 may supportthe outer fitting 120.

Referring to FIGS. 4A through 4F, a method for forming the double-walledtube 70 is shown. In FIG. 4A, a first inner tube 300 may be welded tothe first inner weld lip 102 of the inner fitting 101. The first innertube 300 may be welded to the first inner weld lip 102 using any weldingtechnique. In various embodiments, the first inner weld lip 102 (and allother weld lips of the fitting 100 of FIG. 2A) may instead includethreading or other means for fastening to the various tubes.

In FIG. 4B, a second inner tube 302 may be welded to the second innerweld lip 104 of the inner fitting 101.

In FIG. 4C, the outer fitting 120 may be positioned over and fastened tothe inner fitting 101. For example and with brief reference to FIGS. 2Aand 4C, the outer fitting 120 may be positioned over the inner fitting101 such that the first threading 112 contacts the second threading 132.At this point, the outer fitting 120 may be rotated relative to theinner fitting 101 (i.e., the outer fitting 120 may be torqued) until thefirst threading 112 is mated with the second threading 132. In order tofacilitate this torqueing, a wrench having an interface that mates withthe outward extending protrusion 134 may be used. For example, thewrench may have a hexagonal interface.

In FIG. 4D, a first outer tube 304 may be positioned over the firstinner tube 300. The first outer tube 304 may then be welded to the firstouter weld lip 122.

In FIG. 4E, a second outer tube 306 may be positioned over the secondinner tube 302. The second outer tube 306 may then be welded to thesecond outer weld lip 124. In various embodiments, the double-walledtube 70 may be considered to be completed at this step. In that regard,the first inner tube 300, the second inner tube 302, and the innerfitting 101 may be regarded as the inner tube 312 of the double-walledtube 70. Likewise, the first outer tube 304, the second outer tube 306,and the outer fitting 120 may be regarded as the outer tube 314 of thedouble-walled tube 70.

Referring to FIGS. 4E and 4F, it may be desirable to position fittingson the double-walled tube 70. In particular, a first fitting 308 may becoupled to one or both of the first inner tube 300 or the first outertube 304. Likewise, a second fitting 310 may be coupled to one or bothof the second inner tube 302 or the second outer tube 306. In variousembodiments, the double-walled tube 70 may be considered to be completedat this step.

The fitting 100 may include any of a variety of materials. For example,the fitting 100 may include stainless steel, aluminum, titanium, anaustenitic nickel-chromium-based alloy, such as a composition that byweight contains between 17% and 21% chromium, between 2.8% and 3.3%molybdenum, between 50% to 55% nickel, and between 4.75% and 5.5%niobium (available as INCONEL 718 from the Special Metals CorporationHuntington, W. Va., USA), or the like. It may be desirable for thematerial of the fitting 100 to be the same as the material of the innertubes 300, 302 and the outer tubes 304, 306.

While the disclosure is described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the spirit and scope of the disclosure. In addition,different modifications may be made to adapt the teachings of thedisclosure to particular situations or materials, without departing fromthe essential scope thereof. The disclosure is thus not limited to theparticular examples disclosed herein, but includes all embodimentsfalling within the scope of the appended claims.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosure. The scope of the disclosure is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of a, b, or c” is usedin the claims, it is intended that the phrase be interpreted to meanthat a alone may be present in an embodiment, b alone may be present inan embodiment, c alone may be present in an embodiment, or that anycombination of the elements a, b and c may be present in a singleembodiment; for example, a and b, a and c, b and c, or a and b and c.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”, “anexample embodiment”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it may be within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112(f), unless the element is expressly recitedusing the phrase “means for.” As used herein, the terms “comprises”,“comprising”, or any other variation thereof, are intended to cover anon-exclusive inclusion, such that a process, method, article, orapparatus that comprises a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus.

1. A fitting for forming a double-walled tube, comprising: an innerfitting having a first inner weld lip, a second inner weld lip, and aninner body extending from the first inner weld lip to the second innerweld lip and having an outer surface with a first threading; and anouter fitting having a first outer weld lip, a second outer weld lip,and an outer body extending from the first outer weld lip to the secondouter weld lip and having an inner surface with a second threading thatis configured to mate with the first threading.
 2. The fitting of claim1, wherein the inner fitting further includes at least two bump-outsextending outward from the inner body, and the outer surface with thefirst threading is positioned on an outer surface of the at least twobump-outs.
 3. The fitting of claim 2, wherein a channel is definedbetween the at least two bump-outs when the inner fitting is mated withthe outer fitting to allow fluid to flow between the inner body and theouter body.
 4. The fitting of claim 2, wherein the at least twobump-outs includes three bump-outs.
 5. The fitting of claim 1, whereinthe outer fitting further includes an outward-extending protrusionhaving at least one angle configured to interface with a tool forfastening the outer fitting to the inner fitting.
 6. The fitting ofclaim 5, wherein the outward-extending protrusion has a shape thatcorresponds to a portion of a hexagon.
 7. The fitting of claim 1,wherein a length of the inner fitting from the first inner weld lip tothe second inner weld lip is less than a length of the outer fittingfrom the first outer weld lip to the second outer weld lip.
 8. Adouble-walled tube, comprising: an inner tube having: a first inner tubeand a second inner tube, and an inner fitting having a first inner weldlip configured to be welded to the first inner tube, a second inner weldlip configured to be welded to the second inner tube, and an inner bodyextending from the first inner weld lip to the second inner weld lip andhaving an outer surface with a first threading; and an outer tubehaving: a first outer tube and a second outer tube, and an outer fittinghaving a first outer weld lip configured to be welded to the first outertube, a second outer weld lip configured to be welded to the secondouter tube, and an outer body extending from the first outer weld lip tothe second outer weld lip and having an inner surface with a secondthreading that is configured to mate with the first threading.
 9. Thedouble-walled tube of claim 8, wherein the inner fitting furtherincludes at least two bump-outs extending outward from the inner body,and the outer surface with the first threading is positioned on an outersurface of the at least two bump-outs.
 10. The double-walled tube ofclaim 9, wherein a channel is defined between the at least two bump-outswhen the inner fitting is mated with the outer fitting to allow fluid toflow between the inner body and the outer body.
 11. The double-walledtube of claim 10, wherein the inner tube is configured to transport thefluid and the channel is configured to allow leakage fluid from theinner tube to pass between the outer fitting and the inner fitting. 12.The double-walled tube of claim 9, wherein the at least two bump-outsincludes three bump-outs.
 13. The double-walled tube of claim 8, whereinthe outer fitting further includes an outward-extending protrusionhaving at least one angle configured to interface with a tool forfastening the outer fitting to the inner fitting.
 14. The double-walledtube of claim 13, wherein the outward-extending protrusion has a shapethat corresponds to a portion of a hexagon.
 15. The double-walled tubeof claim 8, wherein a length of the inner fitting from the first innerweld lip to the second inner weld lip is less than a length of the outerfitting from the first outer weld lip to the second outer weld lip.